This invention relates to steam generators and in particular to a fluid cooled spacer for restraining movement of steam heating surface therein.
A portion of the steam superheating surface in large steam generators is frequently in the form of division panels. These panels are made up of a plurality of parallel tubes which are intermeshed and U-shaped and supported from an upper elevation at or above the roof of the furnace. These panels are widely spaced from one another in the order of 8 feet or 12 feet. The panels are large in the order of 30 feet to 40 feet high and 8 feet wide. Minor gas pressure fluctuations therefore exert considerable forces on the panel causing them to tend to swing from side-to-side.
Since there is concern that the repeated swinging of these panels will cause fatigue cracking near the upper support of these panels it is desirable to restrain these panels to minimize this movement. This has been accomplished through the vehicle of using steam cooled spacers which pass horizontally alongside the panels at a lower elevation. These tubes pass on both sides of the panel and serve to maintain the tubes in the plane of the panel as well as providing a vehicle which when restrained will restrain the movement of the division panels.
Towards the rear of the furnace there are normally secondary superheaters which are more closely spaced than the division panels. These are located at a lower gas temperature zone than the division panels and a transverse steam cooled spacer passes through these secondary superheaters and transversely spaces them. This spacer need not be securely fastened to a wall of the furnace, since it engages a large number of the secondary superheaters. The random gas forces applied to the various pendants will tend to offset one another thereby minimizing transverse movement of the entire group of assemblies. One end of the steam cooled spacer surrounding a group of division panels engages a corresponding secondary superheater, thereby restraining one end of the steam cooled spacer.
The other end of the steam cooled spacer is restrained by engagement with the front furnace wall tubes. A pair of tubes is bumped into the furnace to provide a restraining anchor. The fluid cooled spacer is restrained at the front end through engagement with these anchor tubes. The anchor must be arranged to permit the required differential expansion between the various components. The furnace wall and therefore the bumped anchoring tubes will move down as a function of the temperature of the furnace walls. The steam cooled spacer will move down as a function of the temperature of the superheater panels, and will also move towards or away from the front wall as a function of not only the expansion of the roof and supporting structure, but also as a function of the rotation of the various division panels due to temperature differences between the inlet and outlet legs thereof.
The anchor must also be designed to take substantial forces. For instance a pressure differential of 1 inch of water on a single panel which is 8 feet .times. 30 feet in size, amounts to 18,000 lb. force. It follows that the distance which tubes are bumped into the furnace should be minimized since the bending moment on these tubes increases in direct proportion to the length of the applied force from the furnace wall. Accordingly, it has been the practice to extend the steam cooled spacer to a position closely adjacent to the front wall, and to pass it vertically upward between the anchor tubes. By engaging these anchor tubes in either direction the steam cooled spacer has been restrained at the front end.
The extremely high gas temperature in this area in the order of 2200.degree. F. has made it impossible to use conventional structures to perform this function which could be used in a friendlier environment. It was found that by just permitting these tubes to abut one another they wore through rather rapidly. Wearing strips were placed on each of the tubes with the same result. Hardened and specially heat treated wearing strips were added but the life of the anchor structure continued to be low.
It is an object of this invention to provide a spacer tube arrangement and an anchor structure which will function to restrain movement of the division panels and which will have a long life. The vertical portion of the fluid cooled spacer tube has a freely rotatable sleeve mounted thereon at the elevation where the tube contacts the front wall anchor tube. This freely rotatable sleeve is supported between a lower ring which is welded to the spacer tube and supports the sleeve and an upper ring which is welded to the spacer tube and restrains incidental upward movement of the rotatable sleeve. Since the vertical portion of the spacer tube intersects the bumped furnace wall tubes at two elevations in the restraining area a separate sleeve is supplied at each elevation.
The bumped furnace wall tubes which engage the spacer also have sleeves surrounding them. Since these sleeves are placed on the furnace wall tube before bending it to shape, they are not free to rotate. It has been found that despite the apparent lack of efficacious cooling of these sleeves which are not connected with a solid metal path for heat flow, that they survive in this environment longer than an equivalent thickness of wearing strip material would. It now appears that the restraining phenomena must involve not only direct contact but some sliding motion, and the rotatable sleeve is better able to absorb this movement with less wear. Other objects and advantages of this invention will become apparent as the description proceeds.